JPS595071A - Fluid jet printing head - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (6) The present invention relates to a fluid jet printing apparatus, and more particularly to a print head and method for generating at least one drip stream, the invention comprising a print head configuration. and those whose movements are Westernized.

The Geno I drop printer and coating device operates by generating a stream of small droplets of ink or paint fluid and controlling the deposition of the drops onto a print receiving medium. Typically, the drops are electrically charged and then deflected by an electric field. The drip is formed from a fluid filament emerging from a small orifice.

This orifice communicates with a fluid tank in which fluid is maintained under pressure. Each fluid filament tends to break at its tip to form a drip stream. In order for the drops to be accurately deflected by the electric field and selectively deposited on the print-receiving medium of the drops, it is necessary that the drop dimensions and the spacing between drops within each drop stream be substantially -mK. .

Breaking the filament into a drip stream is facilitated by mechanically vibrating some or all of the printhead structure in a process called "stimulation."

(7) One conventional stimulation method is U.S. Pat. No. 878,939 issued June 12, 1973 to Lyon et al.
As shown in No. 8, a representative approximately 4 flexible wall plate of a fluid tank is provided with a fluid orifice, and this wall plate, known as the "orifice plate," is subjected to a series of bending waves that cause this plate to The object is stimulated by moving the object along the path. Although this method produces approximately uniform drip size and spacing, the timing of fluid filament breakage varies along the length of the Oriswiss plate.

Another method is to vibrate the entire printhead, including the ink manifold structure and orifice plate structure, together. This is Beam on June 22, 1971
U.S. Pat. This type of arrangement inevitably fatigues the printhead mounting structure since it is subject to the same vibrations that are applied to the manifold and orifice plates. Additionally, the amplitude and phase of the vibratory motion is difficult to control at frequencies commonly used in jet drop printer operation (8).

Another method for filament stimulation is described in U.S. Pat. No. 409, issued June 13, 1978 to CILα.
No. 5232. Using the technique disclosed in this patent, a stimulator attached to the upper portion of the fluid tank generates pressure waves that propagate downward through the fluid. Each stimulator has a pair of piezoelectric crystal elements that vibrate in phase and are mounted on opposite sides of a mounting plate that coincides with the nodal plane. A reaction mass is disposed at the end of each stimulator opposite the stimulator member that is coupled to the fluid.

This reaction mass ensures that the nodal planes are properly positioned.

GB 1,422,388 discloses a print head in which a piezoelectric crystal element forms one wall of the print head (a single jet inkjet). When a droplet is to be ejected from the orifice, the piezoelectric transducer is electrically activated to create a strain that forces the droplet out of the orifice.

(9) British Patent Specification No. 129 issued October 25, 1972
No. 3980, and Cha on April 15, 1980.
U.S. Pat. No. 4,198,861, published in 1997, discloses a print head in which a pair of piezoelectric crystal elements is bonded to opposite sides of a support plate. A printhead manifold structure is bonded to one of the piezoelectric crystal elements and a four-way counterweight is bonded to the other of the crystal elements. The weight of the counterweight is selected to offset the weight of the printing rad manifold.

Due to this counterbalancing configuration, the support plate is located in the nodal plane when the two piezoelectric transducers are excited synchronously. However, as will be appreciated, the construction of such printheads is relatively complex and it is also difficult to design such printheads to resonate at a desired frequency.

Therefore, the printhead must be tuned after construction so that its resonant frequency is equal to the desired operating frequency.

Finally, U.S. Pat. ing. The length of the nozzle is chosen such that its mechanical resonance frequency is much higher than its driven frequency. The nozzle is in the form of a tube and is surrounded by a piezoelectric ring which, when electrically driven, causes radial contraction and expansion of the tube.

An improved fluid jet print head that can provide uniform in-phase stimulation to multiple jet drip streams, facilitates print head installation, and simplifies print head construction and design. The need exists.

SUMMARY OF THE INVENTION A fluid jet print head for generating at least one drip stream includes an elongated print head body having a length between a first end surface and a second end surface of the print head body. It is considerably larger than its dimensions. The body has a fluid bone at a first end thereof, and the fluid bone has at least one orifice in communication with the tank. Fluid is supplied to the tank under pressure by suitable equipment and exits the tank to form a fluid stream. The transducer device is mounted on the outer surface of the body and extends longitudinally along the body a substantial distance from proximate the support device toward the first end face and the second end face of the body.

The transducer device changes the longitudinal dimension of the body in response to the electrical drive signal, thereby causing mechanical vibration of the body to break the fluid stream into a drip stream.

The transducer device comprises a pair of piezoelectric transducers bonded to opposite sides of the body and extending longitudinally from a location proximate a first end of the body to a location proximate a second end of the body. The piezoelectric transducer provides for alternating expansion and contraction of the elongated printhead body in its longitudinal direction.

The transducer arrangement further includes a device for electrically connecting the pair of transducers in parallel so that the transducers operate in phase and in a direction substantially parallel to the longitudinal direction of the elongated printhead body. Vibration begins to occur. A support device for the printhead locks the printhead body at an intermediate point approximately equidistant from the first and second end surfaces thereof.

In other cases, the transducer arrangement may include a device for electrically connecting the transducers such that the transducers operate out of phase to produce bending waves. A support device for the print head locks the print head body at a distance equal to 0.23 of the respective overall length from each end face of the print head body.

In the case of longitudinally parallel oscillations, the support device may consist of a pair of relatively thin mounting flanges, each formed integrally with the printhead body.

The flange extends from the elongate printhead body on opposite sides thereof and is approximately equidistant from the first and second end faces thereof so as to support the body along the section plane. Alternatively, the support device may include a pair of support studs that engage the printhead body on opposite sides of the body at positions substantially equidistant from the first and second end faces of the printhead body.

The printhead body includes a device defining a slot in a first end face thereof, and an orifice plate device attached to the device defining the slot and with which the fluid bone forms a reservoir. The orifice plate device includes a plurality of orifices for generating a plurality of drip streams. The printhead body further includes a fluid supply opening and a fluid outlet opening communicating with the slot. The fluid jet printhead further includes a fluid conduit coupled to the fluid supply opening and the fluid outlet opening. The fluid conduit is formed of a material that exhibits a significantly different vibrational impedance than the printhead body and therefore does not provide substantial power losses. The fluid conduit may be made of, for example, a polymeric material.

The fluid jet print head further has a structure in which fo = C/, where L is the dimension of the body in the longitudinal direction and C is the speed of sound in the body.
Apparatus may be provided for applying an electrical drive signal of a frequency substantially equal to 2L. In this case, the fluid jet print head is driven at a frequency close to its mechanical resonance frequency.

In the case of bending vibrations, the transducer is driven at a frequency Fo = αCα/L2, where a is the lateral thickness of the printhead body and α-1! =1. It is q.

In this case, the two nodal attachment axes are set at a distance equal to approximately 0.23 of the length of the printing hem body centered between the transducers.

A method for stimulating a rupture in a fluid stream emanating from at least one orifice communicating with a fluid reservoir in a fluid jet print head includes the following steps.

(a) providing an elongated printhead with a tank and an orifice on one end; (b) applying fluid to the tank under pressure to produce fluid flow through the orifice; (c) opposite ends of the elongate printhead. (d) alternately extending and retracting the print head substantially at a resonant frequency of the print head; or so that the print head is supported in the partial plane and the parent fluid flow is effectively stimulated to break into drops.

The resonant frequency of the printhead may be approximately equal to the resonant frequency of the fluid stream. The print head can be expanded and contracted by piezoelectric transducers glued to its outer surface.

Fluid flow may also be stimulated by operating the transducers out of phase to create bending vibrations of the printhead.

In this stimulation method, the print head is mounted at a distance from each end surface approximately equal to 0.23 times the length of the print head.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a fluid jet printhead in which the printhead consists of an elongated body which generates one or more drip streams driven to extend and contract in the longitudinal direction of the printhead; To provide such a print head and method in which the print head is driven by a thin piezoelectric transducer glued to its outer surface, and to provide such a print head in which a support for the print head is provided in a part plane. That's true.

Other objects and advantages of the invention will become apparent from the following description, the accompanying drawings, and the claims.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION This invention relates to fluid jet printheads of the type that can be used for inkjet printing, painting, textile dyeing, and other applications. As is known, devices of this type typically operate by electrically charging the drops in one or more jet drip streams and causing the trajectory of some of the drops to be deflected by an electric field. To generate one or more streams of drips, fluid is typically added under pressure to a fluid tank and flows through one or more orifices or nozzles in communication with the tank.

The fluid emerges from the orifice as a fluid filament that, without perturbation, will break off in a somewhat irregular manner into drops of varying size and spacing. Since it is not possible to charge and deflect such irregular drops, jet infusion devices typically employ some method of mechanical stimulation of the fluid filament so that the filament is generally uniform at the desired drop breakage frequency. (17) The size and spacing of the drip are determined.

A first configuration example of a print head according to the present invention is shown in Fig. 1 (not shown).
7 shown in FIG. The printhead generally consists of an elongated printhead body 1o, the length L of which is considerably larger than the other dimensions α and b. The main body 10 has an orifice plate 12 and a block 14 made of X material. Body 1o
At its first end, the fluid receiver has a tank 16 and also has at least one, preferably a plurality of orifices 18 arranged in a row across the orifice plate 12.

Orifice plate 12 is adhered to a block 14 of material, such as stainless steel, by a suitable adhesive. The block 14 has a slot 2o, which is the orifice plate 1.
2 together form a tank 16. Block 14 further includes a fluid supply opening 22 and a fluid outlet opening 24, both of which communicate with slot 20.

The print head further includes a reservoir device for supplying fluid under pressure to the tank 16 so that the fluid emerges from the orifice 18 as a fluid filament which can be broken to create a drip stream. We are prepared. This includes a pump 26 (iif
I'm getting better. Conduit 32 is connected to fluid outlet 24 so that it can be removed from flow fi flange 6 during cross-flushing of tank 16 when the print head is shut down. As will become clear later on, the end of the printhead to which conduits 3o and 32 are attached, as well as the opposite end of the printhead, breaks the fluid filament and produces drops of uniform size and spacing. The vessel is subjected to mechanical vibrations due to the flow. Conduits 30 and 32 are made of stainless steel block 1
The material is selected from among a number of materials, such as polymeric materials, which have a diagonal impedance substantially different from that of 4. Accordingly, power losses in conductors I# 30 and 32 and resulting vibration damping are minimized.

The print head further includes support devices such as mounting flanges 34. Flange 34 is relatively thin and integrally formed with block 14. Flanges 34 extend from both sides of the A+11 long printhead body 10 and are approximately equidistant VC from the first and second ends of the body. As a result, this flange can be used to support the main body 10 in the partial plane. Flange 34 is therefore not subject to substantial vibration.

The printhead further has a transducer arrangement consisting of thin piezoelectric transducers 36 and 38. These converters are block 14
is adhered to the outside of the body of the body and extends a considerable distance longitudinally along the body from near the support device toward the first and second sides of the body.

Transducers 36 and 38 change size in response to an electrical drive signal applied to line 42 by power source 40, thereby causing mechanical vibration of the body to break the fluid stream into a drip stream.

The piezoelectric transducers 36 and 38 are provided with a conductive coating on their outer surfaces, ie remote from the print head block 14, which forms the first electrode for each of them. A generally grounded metal print head block 14 provides a second electrode for each of these transducers. The piezoelectric transducers are selected to alternately extend and contract along the length of the print head when driven by an alternating current drive signal. As seen in FIG. 3, transducers 36 and 38 are electrically connected in parallel so that the transducers are oriented to extend and retract simultaneously due to the drive signal on line 42. There is.

Since transducers 36 and 38 are glued to block 14, they also expand and contract the block.

If desired, an additional piezoelectric transducer 44 can be glued to one of the narrow sides of the print head to connect the print head block 14.
An output voltage that varies in accordance with the expansion and contraction of the wire 46 may be applied to the wire 46. The amplitude of the signal on line 46 is proportional to the amplitude of the mechanical vibration of block 14.

The mechanism by which the first configuration example of the print head according to the invention operates can be explained as follows. The elongated printhead body is somewhat similar to a conventional coil generator. When such a spring is compressed and then quickly released, it oscillates about its center at a frequency f, called its fundamental longitudinal resonance frequency (21).

In this state, the ends of the spring move toward and away from the center of the spring, and the center remains stationary.

Therefore, if the center of the spring is fixed and the above operation is repeated, the spring will move to the same frequency F. It starts to vibrate.

Steel block 1 forming part of the print head body
4 can be considered a very stiff spring. Therefore, the block 14 can be held in its center, such as by the flange 34, when suitably mechanically stimulated, and its ends can be moved alternately toward and away from the center. Inside the block there is a part plane, so
The seven langes 34 are not subject to substantial vibration, so the printhead supports do not interfere with their operation. The fluid receiver is tank 16
When the end face of the printhead body 1o forming the oscilloscope vibrates, the vibrations are transmitted to the fluid filament exiting the orifice 18, causing a substantially simultaneous uniform drip break. Note that the tank 16 is small compared to the overall dimensions of the block 14 and is centrally located on the end face of the prong.

Therefore, the tank 16 does not interfere much with the vibrations of the block 14, nor does it have any effect on the resonant frequency of the print head.

It can be said generally that the resonant frequency of block 14 is given by fo = C/2L=JE/p/7F.

However, C is the speed of sound in the material of the print head block 14, L is the length of the print head in the longitudinal direction, and E is the length of the block 14.
is the elastic modulus of the material forming the block 14, and ρ is the density of the material forming the block 14.

Preferably, the printhead is designed to operate at or near its resonant frequency, and this frequency is within the appropriate fluid jet stimulation frequency range, e.g. 50 kHz.
Select between z and 100 kHz.

By providing a pair of piezoelectric transducers 36 and 38 on opposite sides of block 14, block 14 will expand and contract without bending vibrations, but if only one piezoelectric transducer were used. That won't happen.

Additionally, using two piezoelectric transducers allows for a higher power input to the print head for a given voltage, and therefore a higher maximum power input to the print head, which may lead to destruction of the piezoelectric transducers. Unfortunately, there is a limit to the voltage difference that can be applied to this without causing damage.

As is well known, E and L are related to temperature, so the resonant frequency of the print head changes with changes in temperature. f vs. temperature change in ΔT at or near room temperature.

The change △f is △f - △f.

It is given by kΔT/2, where k is approximately 4×10−′/C0 for stainless steel.

When dimensions a and b are small compared to L, the print head can be driven at an off-resonance frequency. Figure 5 shows
4.19 X 10-2cm (16,5X 10-”
) illustrates the variation in drive voltage applied to the transducer required to drive a single jet printhead for a constant nominal filament length of . Generally, the nominal filament is a function of drive voltage and drive frequency. For any given drive frequency, the nominal filament length decreases with increasing drive voltage.

As is clear from FIG. 5, the printhead requires a drive voltage of approximately 20 volts peak at a resonant frequency of 83 kHz. When driving with an oscillator at a frequency on either side of the resonant frequency, the filament length should be 4.19 x 10-0-2a 16.5
On either side of the resonant frequency, the required voltage increases approximately linearly with frequency. However, the voltage applied to the piezoelectric transducer As long as this maximum voltage is not exceeded, the transducer can be driven in the positive slope part of the curve in Figure 5 or in the negative slope part of the curve.If the resonant frequency remains constant, then Assuming that such variations can be compensated for by varying the drive frequency synchronously with variations in the speed of the print-receiving medium on which the drops from the print head are to be deposited. (25) However, the frequency of the drive signal is monitored and the voltage of the drive signal is adjusted appropriately to compensate for frequency deviations and maintain the desired fluid filament length.

If desired, additional piezoelectric transducers 44 can be utilized to monitor the frequency of the drive signal and the amplitude of the printhead vibrations. In Figure 6, 4.19 x 10-2
The length of CTn (16,5X 10-”') is approximately 2.54
The electrical specific power at line 46 is plotted against the frequency of the drive signal to maintain a nominal fluid filament of a single jet printhead of diameter x 100-3a (approximately I x 10-""). Assuming no change in the resonant frequency of the print head or jet, the output voltage and frequency at line 46 can be monitored to maintain the output voltage at line 46 at the reference voltage level specified by the curve of FIG. The desired length of the fluid filament can be maintained by adjusting the level of drive signal required.

As will be appreciated, numerous modifications can be made to the disclosed printhead (26) without departing from the scope of the present invention. For example, flange 34 may be deleted. Other devices, such as support screws, may be provided for attaching the printhead to a suitable support structure, even if the attachment point is substantially in the nodal plane midway between the ends of the printhead body 10. do it.

Reference is now made to FIG. 7 illustrating a circuit providing an apparatus for providing electrical drive signals. The output of fixed circular wavenumber oscillator 48 is provided to converters 36 and 38 via voltage controlled attenuator circuit 50, power amplifier 52, and step-up transformer 54. The output from transducer 44 on line 46 is used to control the amount of attenuation provided by circuit 50. 8
The signal at 46 is amplified by amplifier 56, converted to a DC signal by converter 58, and compared with a selection reference signal by Calo matching circuit 60 to generate a line 621C signal, which signal receives the attenuation provided by circuit 50. Control. This feedback configuration allows line 42
The amplitude of the drive signal at and the amplitude of the mechanical vibration of the print head are precisely controlled.

FIG. 8 is a side view illustrating a second configuration example of the present invention, in which elements corresponding to the print head of FIG. 1 are given the same reference numerals. In this configuration, transducers 36 and 38 are oriented such that a positive drive signal on line 42 causes one transducer to extend and the other transducer to contract, and a negative drive signal to do the opposite. is attached to the print head body. Therefore, the AC drive signal is
The print head is caused to vibrate in its first bending mode. This mode of vibration is illustrated in FIG. 8 by intermediate line 64, which shows the range of movement of the center of printhead body 14, although the bending is greatly exaggerated for clarity. It should be noted that line 64 intersects at a point approximately 0.23Z inwardly from each end face of the printhead body, thus indicating a nodal point. A mounting hole 66 is drilled into the body 14 at this node, and a second corresponding pair of mounting holes are drilled on the opposite side of the printhead body.

By providing a mounting pin that extends into the hole 66, a pivot support is provided that does not impede bending movement of the print head.

This bending mode can be excited by driving the transducer at a frequency Fo-αCa/L2C, where α is about 1.76.

This formula is a simplified version of the following resonant frequency equation.

Fo-π9 CK/8L2 where K is the radius of rotation and is equal to α/2 for the illustrated print head.

It will further be appreciated that this invention is not limited to the precise form of method and apparatus disclosed, and that abstract changes may be made therein without departing from the scope of this invention. can.

[Brief explanation of the drawing]

FIG. 1 shows a first diagram of a fluid jet printing head according to the present invention.
FIG. 3 is an exploded view showing a configuration example. FIG. 2 is a plan view of the print head of FIG. 1 (29) with the orifice plate removed. 3 is a side view of the printhead of FIG. 1 with electrical drive circuitry; FIG. FIG. 4 is an enlarged partial cross-sectional view taken generally along line 4--4 of FIG. FIG. 5 is a diagram useful in explaining the operation of a printhead according to the invention. ' Figure 6 is a diagram useful in explaining the operation of the printhead according to the invention. FIG. 7 is a schematic diagram illustrating the drive circuitry for a six-fluid jet print head. FIG. 8 shows a second diagram of a fluid jet print head according to the present invention.
FIG. 3 is a side view of a configuration example. In these figures, 10 is an elongated print head body;
12 is an orifice plate, 14 is a block, 16 is a fluid receiver, 18 is an orifice, 20 is a slot, 22 is a fluid supply opening, 24 is a fluid outlet opening, 30 is a fluid conduit,
32 is a conduit, 34 is a mounting flange, 36.38 is a piezoelectric transducer, and 44 is a monitoring piezoelectric transducer. r30) ■, 11 numbers (revised) FIG-6.

Claims (1)

Claims: (1) an elongated printhead body having a length between a first end surface and a second end surface that is substantially greater than other dimensions thereof; a fluid receiver having a tank on a first end face of said body and said fluid receiver having at least one orifice in communication with said body; a support device for locking the printhead body intermediate the first end surface and the second end surface; and a support device attached to the outer surface of the body. said body. extending a substantial distance along the length of the body and changing the longitudinal dimension of the body in response to an electrical drive signal to cause mechanical vibration of the body; A fluid jet print head for generating at least one stream of drops, comprising a transducer device for breaking the stream into a stream of drops (1). (2) said transducer device comprises a pair of piezoelectric actuators bonded to opposite sides of said body and extending longitudinally from a location proximate said first end surface to a location proximate said second end surface; A fluid jet print head as claimed in claim 1, comprising a transducer. 3. The fluid jet printhead of claim 2, wherein said piezoelectric transducer provides alternating expansion and contraction in the longitudinal direction of said elongated printhead body. (4) the transducer device further includes a device for electrically connecting the pair of piezoelectric transducers in parallel;
A fluid jet print head according to claim 3. 5. The fluid jet print head of claim 4, wherein the piezoelectric transducers are connected to expand and contract in phase. (6) The support device holds the print head body (2).
6. A fluid jet print head according to claim 5, wherein the fluid jet print head is anchored at a midpoint substantially equidistant from said first and second end surfaces thereof. (7) Said piezoelectric transducer is connected to expand and contract out of phase so as to cause bending of said printhead body.
Fluid jet printing head as described in Section. 8. The fluid jet printhead of claim 7, wherein said support device pivotably supports said printhead body at a bending node. (9) said support device comprises a pair of relatively thin mounting flanges, each integrally formed with said printhead body, and said flanges are mounted on opposite sides of said elongated printhead body; The first part of the main body
2. A fluid jet printhead as claimed in claim 1, wherein the flange extends substantially equidistantly from an end and a second end, the flange supporting the body along a nodal plane. . (3) (10) a pair of support devices locking the printhead body at positions substantially equidistant from the first and second end faces of the body on opposite sides of the printhead body; A fluid jet print head as claimed in claim 1, comprising a support screw. (11) an orifice plate arrangement in which said printhead body defines a slot at a first end thereof, and an orifice plate arrangement attached to said slot defining arrangement and with which said fluid receptacle forms a tank; A fluid jet print head as claimed in claim 1, comprising: (2) The fluid jet print head of claim 11, wherein the orifice plate arrangement comprises a plurality of orifices for generating a plurality of drip streams. (13) The print head comprises: 12. The fluid jet print head of claim 11, further comprising a fluid outlet opening in communication with said slot. (14) said fluid supply opening and said fluid outlet opening. further comprising a coupled fluid conduit, (4) the fluid conduit being formed of a material exhibiting a significantly different vibrational impedance than the printhead body, such that the fluid conduit is 14. The fluid jet print head of claim 13, wherein the fluid jet print head is adapted to provide no substantial power losses. 16. The fluid jet print head of claim 15, further comprising a monitoring transducer device attached to an exterior surface of the body for providing an electrical monitoring signal in response to dimensional changes in the body. (17) where L is the longitudinal dimension of said body and C is the speed of sound in said body, then f,=C. /2L for applying an electrical drive signal of a frequency substantially equal to f., thereby driving the fluid jet print head at a frequency substantially equal to its mechanical resonant frequency. 5) a fluid jet print head as claimed in claim 5, wherein the fluid jet printhead is adapted to: (18) be mounted on an exterior surface of said body and adapted to provide electrical monitoring in response to dimensional changes in said body; further comprising: a monitoring transducer device for providing a signal; and, responsive to the monitoring transducer device, a device for applying to the converter device an electrical drive signal of an amplitude dependent on the electrical monitoring signal. (19) where L is the longitudinal dimension of said body, C is the speed of sound in said body, and K is the rotation of said body. A fluid jet as claimed in claim 7, further comprising means for applying an electrical drive signal of a frequency substantially equal to FO, where FO = 90/8 L2 when pointing at a radius. Print herad.